Effect Of Selenium (?) On The Methane Production Efficiency Of Anaerobic Digestion Of Pig Manure

Selenium is widely used in animal feed to regulate the growth and development of animals,but most of the selenium intaked by livestock and poultry excreted in vitro,which caused serious ecological risks to the environment.Anaerobic digestion of livestock and poultry manure has been proved to be the most effective resource processing technology.Recently literature reported that selenium inhibits the activity of methanogenic microorganisms in anaerobic digestion system,and whereas information on the effect of selenium-containing manure on the subsequent anaerobic digestion process is still lacking.In this paper,the effects of inorganic selenium???on the anaerobic digestion process including the activity of anaerobic microorganisms,gas production efficiency and process stability and anaerobic microbial flora were studied.And mechanism of inorganic selenium???inhibiting the anaerobic digestion process was determined.The conclusions are as follows:?1?By studying effect of selenium with different initial concentration on the biogas production efficiency of mesophilic anaerobic digestion of pig manure,the results showed that low concentration of 5mgSe⁴⁺/kg promoted the methane production and methane production rate.The high concentration of Se⁴⁺could inhibit the activity of methane and reduce amount of methane production and the methane production rate;with the increase of concentration,the degree of inhibition gradually increased,or even completely inhibited.Through the methanogenic activity recovery experiment,it was found that Se⁴⁺was a metabolic toxicity.The effects of different concentrations of selenium on the anaerobic production of methane in pig manure were simulated by the first-order kinetics and gompertz model,but the Gompertz model simulation results is better.?2?By studying effect of selenium with different initial concentration on the stability of anaerobic digestion process of pig manure,results showed that the addition of Se⁴⁺have a slight effect on the pH during the anaerobic digestion of pig manure.The low concentration of Se⁴⁺has little effect on the system VFA_s,and the accumulation of VFA_s is alleviated at the early stage of digestion.The low concentration of Se⁴⁺can accelerate the degradation rate of nitrogenous organic matter,NH₄⁺-N release speed,resulting in increased system TA content,rapid degradation of organic matter;The addition of high concentration of Se⁴⁺resulted in the accumulation of VFA_s,slowed down the degradation rate of nitrogenous organic matter,slowed down the release rate of NH₄⁺-N,decreased the content of TA.With the inhibition of Se⁴⁺weakened,methanogenic bacteria activity gradually recovered,VFAs content decreased rapidly,the system gas production rate began to accelerate.?3?By studying effect of selenium with different initial concentration on anaerobic microbial flora,results showed that the addition of low concentration of Se⁴⁺increased the diversity of microorganisms.The addition of high concentration of Se⁴⁺could decrease the diversity of microbes,but the microbial activity was increased due to the decrease of Se⁴⁺inhibition and the recovery of microbial activity in the later stage of digestion.The low concentration of Se⁴⁺had little effect on the community structure.At this point mainly with Firmicutes and Proteobacteria.At this time,the effect of high concentration of Se⁴⁺on the digestion stage was not significant,but at the later stage of digestion,the community structure became complicated,Firmicutes?Proteobacteria and Bacteroidetes,but there are some others including the Chloroflexi,Cloacimonetes,Synergistetes in this community structure.?4?The effect of selenium on anaerobic digestion in different carbon source environment was studied.Results showed that anaerobic digestion process is inhibited to the stage of anaerobic methane production in this case of not adding Se⁴⁺;The addition of Se⁴⁺has a certain degree of inhibition in anaerobic digestion of pig manure wastewater,which for the hydrolysis of digestion and the production of methane inhibition is slightly stronger than hydrogen production of acetic acid and methane production stage in the digestion stage.In these three stages of anaerobic microorganisms may be the first selenium conversion,and then the process of methane production.